In certain specialized areas of sewing in a commercial facility particularly as occurs in the sewing of seat covers for automobiles, it often occurs that the seam being sewn is on meshing workpieces where one work piece is at a considerably different elevation than the other workpiece. When that occurs the operator is compelled to try to balance the sole plates so that one sole plate rides on the higher workpiece while the other sole plate is unsupported above the lower workpiece. The difficulty is obvious and various inventive concepts have been put forward to solve the problem.
The patent to Rontke, U.S. Pat. No. 621,145, shows a pair of sole plates which are longitudinally spaced but which also allow transverse vertical sliding with respect to each other. The particular structure shown does not solve the problem of transverse elevation differential but the concept illustrated in the patent could be applied in that fashion.
The patent to Seavers et al, U.S. Pat. No. 1,852,482, shows the problem in FIG. 4 and the solution suggested by the patent is to have one of the sole plates vertically biased to its lower position by a spring while the other sole plate is maintained in rigid position.
The patent to Bouwkamp et al, U.S. Pat. No. 2,481,286, shows a pair of presser feet which are mounted transversely of a center post and are allowed to adjust vertically according to the pivoting lever which pivots from the center post and allows vertical movement of the two transversely aligned presser feet.
The patent to Enos, U.S. Pat. No. 2,652,016, illustrates another embodiment using a spring bias of one of the sole plates of the presser foot to move with respect to the other rigidly mounted sole plate.
The patent to Pisano, U.S. Pat. No. 2,807,225, uses a pair of coil springs for one sole plate to allow its vertical movement with respect to the other sole plate which is rigidly mounted. A patent to Godsen, U.S. Pat. No. 3,796,132, has a similar inventive concept.
In summary, the prior patents illustrate the concept of a pressor foot with one of its sole plates rigidly mounted while the other is allowed to move vertically and is biased into place in some instances by a spring.